Some conventional methods for cooling an electric machine include passing a coolant around a perimeter of the electric machine. The coolant extracts heat from portions of the electric machine, which can lead to electric machine cooling. The configuration of some conventional electric machines can lead to at least partially reduced heat rejection efficiency from different machine elements, such as a stator assembly. In addition, some elements of the machine that can conduct heat energy, such as the stator assembly, may not be properly configured to more efficiently conduct heat energy, which can result in an interface resistance.
Some conventional machines may also conduct heat energy through a rotor assembly. For example, if the machine's rotor assembly generates a significant amount of heat energy, which is common with some electric machines, the rotor assembly heat can be conducted through the machine's shaft and bearings or lost by forced convection to the internal air within the housing. Conducting heat through the bearings can reduce for bearing life, and the conduction resistance of this path can be generally high. Also, the convection resistance from the internal air to the machine's housing can be generally high, which makes this a generally ineffective way to reject heat from the rotor assembly.